It is oftentimes essential in a variety of areas, for example the aerospace field, to have articles of manufacture and articles having a coating thereon which have low temperature expansion coefficients (TEC). Such articles have critical dimensions and for the satisfactory function of such articles it is necessary that such critical dimensions do not change during environmental changes such as temperature. Such articles include microwave filters, feedhorns, wave guides, and spacecraft structures (e.g. solar arrays, reflectors, etc.).
As is known in the art, such thermostable hardware is, in general, made from low thermal expansion coefficient alloys, such as nickel-iron alloys. However, such articles, for example, microwave filters, have heretofore been machined from the raw metal. Such a method is expensive and time-consuming, and very inefficient. Therefore, prior art workers have attempted to make such articles by electroforming either copper or nickel. Since both copper and nickel have relatively high temperature expansion coefficents (e.g. copper has 9.8.times.10.sup.-6 O in/in/.degree.F., and nickel has 8.6.times.10.sup.-6 in/in.degree.F.), this method is unsuitable for those articles requiring temperature expansion coefficients on the order of 5.times.10.sup.-6 or less. For these articles requiring such low temperature expansion coefficients, fabrication of such articles has been accomplished by machining the articles from low temperature expansion coefficient alloys such as invar (an alloy or iron and nickel containing about 36%, by weight of nickel and 64% by weight, of iron). The reason it is necessary to machine articles having low temperature coefficients of expansion rather than electroforming such articles is because the prior art workers have not been able to discover a process for electrodepositing, for example, iron and nickel alloys having low temperature expansion coefficients on the order of 5.times.10.sup.-6 in/in/.degree.F. It should be noted, however, that electrodepositing alloys of nickel and iron has been done in the past. However, almost all of the previous work has been in electrodepositing very thin nickel and iron films for magnetic memory application.